Shinobu was your little sister. After your parents died you and Kanae raises her, trying everything to give her a good life.

Both three of you were training to become a Demon Slayer, even tho you didn't like the idea of Shinobu becoming one too. You were afraid she'll get hurt, or worse..

She was practicing her movements with her sword, since she was short and not that strong she could only kill with poision and couldn't cut off a demon's head.